This invention relates to quickly providing and maintaining hot water to remote faucets in residential and small commercial buildings.
The issue being addressed is the waste of water and time running water down the drain while waiting for hot water from the heater to arrive at remote faucets. In installations with long pipe runs, such as ranch style homes, this can result in a wait of one to two minutes. Tests conducted on a typical ranch style home have shown a waste of 10 to 12 liters of water at each occurrence. In these days of water and energy shortages, the need to eliminate this waste has become more acute.
The requirement for a method to quickly provide hot water at remote faucets has long been known, with devices patented in the early years of the twentieth century. These and subsequent devices were not broadly accepted since they were too complex, their installation was difficult, or they did not function well. Methods to solve this problem have generally followed two different approaches; (1) water circulation systems that continuously or periodically circulate hot water from the heater to the remote faucet and back to the heater through a separate return line, and (2) auxiliary remote water heaters, either in the basement near the faucet, or under the counter at the sink.
One circulation approach is convective flow using sloping hot water supply and return pipes, as shown in U.S. Pat. No. 3,929,153 to Hasty, 30 Dec., 1975, U.S. Pat. No. 2,255,460 to Weaver, 7 May, 1940 and U.S. Pat. No. 3,097,661 to Lee, 16 Jul., 1963. These systems are functional, but are insensitive to user needs, circulating hot water at all times, even at night and when inhabitants are away. Sloping pipes are easily installed in new construction, but are difficult in existing buildings. The return pipe must be of a diameter essentially equal to the supply pipe since convective pressure is extremely low, and flow would be limited with a small return tube. Considerable heat is lost since the surface area of the return pipe is large and stays hot at all times. These systems also have a tendency to excessively heat the cold water pipe which causes a similar problem in the cold water system that they are intended to solve in the hot water system.
Pumps used for hot water circulation as shown in U.S. Pat. No. 3,669,351 to Meier and Carouge, 13 Jun., 1972 and U.S. Pat. No. 4,142,515 to Skaats, 6 Mar., 1979 are also functional, but require electrical power, wiring, motors, seals, switches, and timers or thermostats. They may be more suitable for large commercial buildings than residential applications. Pump operated systems controlled by timers are also insensitive to user needs resulting in wasted heat when hot water is not required. Since pumped circulation systems have many operating parts, reliability will be affected, and maintenance could be an issue. Due to their complexity, initial procurement and installation costs are also high. Operational cost will be experienced to power the pump motor, and noise from the pump may be objectionable to some people.
Auxiliary heaters as shown in U.S. Pat. No. 4,236,548 to Howard, 2 Dec., 1980 can be used to provide instant hot water to remote outlets, however the cost of initial procurement and installation is a significant drawback. They require connection to gas (and necessary vent stack) or electricity for their energy source. Operational costs will also be incurred. Heaters made for installation under the counter are designed to serve extremely hot water (approximately 80 to 85 degrees C.) for direct use in coffee, tea or soups without further heating. These heaters usually contain only a small volume of hot water (3 to 5 liters), and constitute a potential safety hazard due to their extreme temperature.
The recently patented Dual Mode Hot Water Circulation Apparatus (U.S. Pat. No. 5,331,996--26 Jul., 1994, to R. G. Ziehm) uses a cold water heat exchanger to induce a low rate convective circulation flow, plus an aspirator to supplement the convective flow with a higher rate circulation flow in response to water use in the building. This system yields excellent results, with hot water immediately available at any time, day or night. The length of the heat exchanger requires a space 1 to 1.5 meters long at an angle to the horizontal where the unit can be installed in the water supply pipe. This space may not always be available. Although the Dual Mode Hot Water Circulation Apparatus performs extremely well, material and manufacturing costs for it will be higher than for the present invention.